The present invention relates to heat sensitive devices and, more particularly, to a heat sensitive cable and method of making same.
Heat sensitive cables which are characterized by the use of semiconductive materials having inverse temperature-resistance characteristics in conjunction with dissimilar thermoelectric conductors are now well known in the art. Such constructions are particularly suitable where it is desired to monitor the greatest temperature existing along the length of the cable, and are exemplified in connection with a system for measuring and locating temperature conditions of interest in U.S. Pat. No. 3,408,607. Thermister cables which are characterized by a core of semi-conductive material surrounded by a mass of temperature-resistant electrically-insulating material covered with a protective metallic sheath are also well known in the art.
Despite the clear advantages and many applications for such cables, they have simply not evolved to the point of providing the desired degree of versatility. It has remained to develop a heat sensitive cable capable of generating a measurable and predictable voltage when the entire length of cable is at ambient whether ambient be at -20.degree. F., 1650.degree. F., or some value therebetween. If this could be achieved with an inverse temperature-resistance material, the thermoelectric output of the cable or a section thereof would be altered in a predictable fashion when subjected to a temperature greater than ambient.
Moreover, if this could be achieved, the cable location where the increase in temperature takes place could be located electronically. This could be achieved, for instance, as fully disclosed and claimed in copending U.S. Ser. No. 887,089 filed Mar. 16, 1978, now U.S. Pat. No. 4,324,138, issued Apr. 13, 1982, for a method of and apparatus and system for determining temperature conditions. As set forth therein, the applications are virtually limitless.
While the value of heat sensitive cable has long been recognized, it has remained to provide such a cable having the requisite versatility for the many applications to be benefited by use thereof. In fact, despite my many prior inventions in this field, as exemplified by U.S. Pat. Nos. 3,408,607 and 3,513,432, the missing link to providing a highly versatile cable has remained. Despite the advantages that will be recognized by those skilled in the art, heat sensitive cable which is operable over a temperature range of between approximately -20.degree. F. and 1650.degree. F. has simply not been available.
It is therefore an object of the present invention to provide a heat sensitive cable operable over a temperature range of between approximately -20.degree. F. and 1650.degree. F.
It is also an object of the present invention to provide a cable of the type described utilizing a material having an insulation resistance within the indicated temperature range variable with temperature in the range of between approximately 100 and 50,000 ohms.
It is a further object of the present invention to provide a cable of the type described which comprises a thermocouple temperature monitoring device having a metallic tubular sheath containing two dissimilar metal thermocouple wires packed in a semiconductive ceramic powder.
It is another object of the present invention to provide a cable of the type described wherein the thermocouple wires surrounded by semiconductive ceramic powder are spaced equidistant from each other and the outer sheath.
It is still another object of the present invention to provide a cable of the type described which is passive and self-generating to generate a voltage potential between the thermocouple wires indicative of the temperature existing along its entire length or at the hottest point along its length if the temperatures are unequal.
It is still another object of the present invention to provide a cable of the type described capable of precise, non-perishable, reproducible measurement of the temperature and identification of the location of the hottest spot when monitoring with a high input impedance temperature device.
It is another object of the present invention to provide a cable of the type described wherein the tubular sheath and the thermocouple wires can be formed of various materials and combinations of materials to yield various mechanical properties and temperature-voltage response curves.
It is a further object of the present invention to provide a cable of the type described which can be produced in lengths of thousands of feet at a fraction of the cost of making other types or constructions of heat sensitive cable.
An additional object of the present invention is to provide a cable of the type described utilizing commercially available materials and processes to manufacture the cable.
These and other objects, advantages and feature of the present invention will be apparent from a consideration of the accompanying specification, claims and drawings.